The invention relates to a shaped charge capsule.
Referring to FIG. 1, a perforating gun 8 typically is used to form tunnels in a formation to enhance the production of oil and/or gas from the formation. These tunnels are formed by detonating shaped charges that are housed by shaped charge capsules (shaped charge capsules 10a, 10b and 10c shown as examples) of the perforating gun 8. As depicted in FIG. 1, the shaped charge capsules typically are oriented in radially outward directions and are arranged in a helical, or spiral, phasing pattern.
Although the shaped charge typically is a secondary explosive that is difficult to detonate without the use of a primary explosive, features of the shaped charge capsule may increase the likelihood of accidental detonation. For example, the shaped charge capsule typically is hermetically sealed to prevent the hydrostatic pressure of the fluid in the well from accidentally detonating the shaped charge that is housed inside. However, if the shaped charge capsule is exposed to fire (during transport of the shaped charge capsule, for example), this seal may cause a significant increase in the internal pressure of the shaped charge capsule. This pressure buildup, in turn, may cause accidental detonation of the shaped charge.
Referring to FIG. 2, a conventional shaped charge capsule 5 that is designed to permit venting of excess internal pressure in the case of fire may include a cap 11 that covers the open end of a cup-shaped charge casing 7. A plastic ring 9 resides in an external groove of the casing 7, and the cap 11 fits over the ring 9. Due to this arrangement, the cap 11 may be crimped so that the ring 9 secures the cap 11 to the casing 7. If a fire occurs, the ring 9 melts to release the cap 11 from the casing 7 and thus, permit any internal gases to vent.
It may be desirable for the cap of the shaped charge capsule to be brittle, a characteristic that minimizes the interference of the cap with a perforation jet that is formed by the detonation of the shaped charge. Unfortunately, the above-described arrangement does not permit the cap 11 to be brittle, as the cap 11 is crimped over the ring 9 to secure the cap 11 to the casing 7.
Thus, there is a continuing need to address one or more of the above-stated problems.
In one embodiment of the invention, a charge capsule includes an open-ended casing and a ring. The casing is adapted to house an explosive, and the casing includes a shoulder to receive a cap to close the casing. A rim of the casing at least partially surrounds the shoulder. The ring is adapted to be placed radially inside the rim and crimped with the rim to secure the cap to the casing. The ring is adapted to melt above an approximate predetermined temperature to release the cap from the casing.
In another embodiment, a method includes providing a ring that is adapted to melt above an approximate predetermined temperature threshold and placing the ring around the approximate periphery of a cap of a shaped charge capsule. A casing of the shaped charge capsule is crimped over the ring and the cap so that the cap is secured to the casing until a temperature of the ring exceeds the temperature threshold.
In yet another embodiment, a method includes providing an adhesive that is adapted to decompose above an approximate predetermined temperature threshold. The adhesive is used to secure a cap of shaped charge capsule to a casing of the shaped charge capsule so that the cap is secured to the casing until a temperature of the ring exceeds the temperature threshold.
Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims.